Optical detecting and ranging system for automotive vehicles

ABSTRACT

A mechanical automatic gain control for a high-frequency detecting and ranging system of the short range type in which the axis of the transmitter is displaced relative to the axis of the receiver to linearize the strength of the received signal over the operating ranges of the system. The system may be used as a range or range rate finder in automotive vehicles in order to determine the distance or range and the range rate or relative velocity between a vehicle in which the system is located and the preceding vehicle. The transmitter transmits high-frequency electromagnetic energy, preferably in the infrared region, toward the rear of the preceding vehicle. This electromagnetic energy is reflected by the reflective lens systems found on the rear of conventional vehicles directionally back toward the transmitter. A small portion of this energy finds its way to the receiver which, as stated above, is displaced from the transmitter. It has been found that the strength or amplitude of the received signal does not vary inversely with the fourth power of the range, as is the case in conventional detecting and ranging systems, but may vary from values of 10 to 100.

United States Patent [72] Inventor Gerald C. Scott Ann Arbor. Mich.

(21] Appl No. 839,346

{22) Filed July 7,1969

[45] Patented Sept. 14, 1971 [73 Assignee Ford Motor Company Dearborn,Mich.

[541 OPTICAL DETECTING AND RANGING SYSTEM FOR AUTOMOTIVE VEHICLES 8Claims, 6 Drawing Figs.

[52] US Cl 356/28, 356/5 [5t] |nt.Cl G0lp 3/36 [50] Field of Search343/8; 356/5, 28

[56] References Cited UNITED STATES PATENTS 2970310 I/l96l Bruce 356/5 X3,l l8,l39 H1964 Durstewitz 356/28 3.164,!25 l/l965 StraubW. 356/5 3.5 I7.998 6/1970 Pryor 356/28 Primary Examiner- Malcolm F. HublerArrorneysJohn R. Faulkner and Keith L. Zerschling ABSTRACT: A mechanicalautomatic gain control for a highfrequency detecting and ranging systemof the short range type in which the axis of the transmitter isdisplaced relative to the axis of the receiver to linearize the strengthof the received signal over the operating ranges of the system. Thesystem may be used as a range or range rate finder in automotivevehicles in order to determine the distance or range and the range rateor relative velocity between a vehicle in which the system is locatedand the preceding vehicle. The transmitter transmits high-frequencyelectromagnetic energy, preferably in the infrared region, toward therear of the preceding vehicle. This electromagnetic energy is reflectedby the reflective lens systems found on the rear of conventionalvehicles directionally back toward the transmitter A small portion ofthis energy finds its way to the receiver which, as stated above, isdisplaced from the transmitter. It has been found that the strength oramplitude of the received signal does not vary in versely with thefourth power of the range, as is the case in conventional detecting andranging systems, but may vary from values of 10 to I00.

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INVENTOR 656410 C JC'OTT OPTICAL DETECTING AND RANGING SYSTEM FORAUTOMOTIVE VEHICLES BACKGROUND OF THE INVENTION In conventionaldetecting and ranging systems, the received signal strength normallyvaries inversely as the fourth power of the range. In short rangedetecting and ranging systems, this presents a severe problem inproperly handling these signals which may have a ratio of the maximumamplitude or signal strength at very short ranges to a minimum amplitudeor signal strength at the longer ranges to a minimum amplitude or signalstrength at the longer ranges of approximately GXIO'. This ratio wouldapply where the detecting and ranging system is designed to operate inthe range of 3 to I50 feet. Normally, sophisticated electrical circuitsare used to limit this ratio to some acceptable value where it may behandled properly by electronic circuitry to compute both range and rangerate.

In the present invention, this ratio of 6X10, for example, has beenreduced in practice to values of IO to 100 and ideally can be reduced toI. This reduction is achieved by proper relative placement of thetransmitter and the receiver and the use of high frequency signals,preferably in the infrared ranges.

SUM MARY OF THE INVENTION When used as an automotive detecting andranging system, the primary target for the detecting and ranging systemof the present invention is the standard conventional retroreflector onthe rear of a preceding vehicle which is designed to reflect light fromthe headlamps of the vehicle immediately behind it. These reflectors areof the optical corner cube type that very directionally reflect thelight back to its source in a narrow beam.

If the receiver of this system were to be located on the transmittingaxis of the transmitter, the amplitude or strength of the receivedsignal would vary substantially inversely as the fourth power of therange. In the present invention, however, the receiver is located apredetermined distance from the transmitter, measured transversely withrespect to the longitudinal axis of the vehicle, the direction ofmovement of the vehicle and the direction of the transmitted signal. Asa result, the amplitude of the received signal will vary less stronglywith range. It has been found that the variance of the strength of thereceived signal with range is strikingly linear when it is consideredthat if the transmitter and receiver were positioned on the same axis,the strength of the received signal would vary inversely as the fourthpower of range. In automotive applications, the ranges of interest maybe from 3 to I50 feet and if the ratio of the strength of the maximumsignal received to the minimum signal received due to these differentranges, vary as the fourth power of the range, the ratio would be of theorder of 6 XIO. In the present invention with the receiver axisdisplaced 6 inches from the transmitter axis, this ratio has beenreduced to I00, and with the receiver axis displaced 10 inches from thetransmitter axis, this ratio has been reduced to II).

The automatic gain control feature of the present invention depends forits operation on the fact that the conventional reflectors found onautomotive vehicles are of the optical corner cube type, or some similartype, that very directionally reflect light back to its source. In theconventional vehicle being produced today, these corner cube reflectorsare comprised of a series of cubes having a dimension of approximatelyone-sixteenth of an inch or 1.6 millimeters. In order for the automaticgain control feature of the present invention to achieve theabove-mentioned results of substantially linearizing the received signalwith respect to range, the transmitted signal should have a wave lengthno longer than about one-sixteenth inch or about L6 millimeters. Thistranslated into frequency amounts to approximately 0.5 kilomegacyclesper second, and hence, is above the operating frequencies ofconventional radio detecting and ranging systems. The frequency rangeover which the system of the present invention is operated is such thatthe wave length of the transmitted electromagnetic energy is in theoptical region of the electromagnetic spectrum and in the range of fromabout L6 mm. to 4Xl0 mm. It is preferable to operate the detecting andranging system so that it transmits infrared electromagnetic energyhaving a wave length encompassed within the range of wave lengths givenabove.

An object of the present invention is the provision of a mechanicalautomatic gain control system for a high frequency detecting and rangingsystem.

A further object of the invention is the provision of mechanicalautomatic gain control for a high frequency dctecting and ranging systemthat may be used in automotive vehicles to determine very short ranges.

A further object of the invention is the provision of means in a highfrequency detecting and ranging system for reducing the large ratios inthe magnitude or strength of the received signals due to variations inthe range from the system to the target.

Other objects and attendant advantages of the present invention may bemore readily realized when the specification is considered in connectionwith the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic representationshowing the transmitter and receiver of the detecting and ranging systemof the present invention mounted in an automotive vehicle andtransmitting electromagnetic energy toward a preceding vehicle;

FIG. 2 is a partial view of a conventional reflector positioned at therear of an automotive vehicle;

FIG. 3 is a sectional view through the reflector shown in FIG. 2;

FIG. 4 is a plot showing the relative strengths of signals received fromthe reflector shown in FIGS. 2 and 3 as the reflector is rotated abouteither a central horizontal or a central vertical axis;

FIG. 5 is a series of curves showing the strength of the received signalas a function of range in a conventional radio detecting and rangingsystem and in the detecting and ranging system of the present invention;and

FIG. 6 is a schematic view showing the transmitter, the receiver and thereflector of the detecting and ranging system of the present inventiontogether with a representation of the transmitted and reflectedelectromagnetic energy.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings inwhich like reference numerals designate like parts throughout theseveral views thereof, there is shown in FIG. 1 an automotive vehicleIt] having a transmitter 12 mounted therein for directingelectromagnetic energy in a direction generally parallel to thelongitudinal axis of the vehicle and to its direction of movement. Areceiver 14 is also mounted in the vehicle [0 for receiving thereflected electromagnetic energy that is transmitted by the transmitterl0 and is reflected back toward the transmitter II from reflectors l6and I8 mounted in the rear of a preceding vehicle 20. The receiver 14has a computer 22 which will compute range and range rate between thevehicle I0 and the vehicle 20. This information may be used to controlthe speed of the vehicle through means not shown. The device 24 may be aspeed selector for this means.

The reflectors l6 and 18 mounted in the preceding vehicle 20 are thoseconventionally used in automotive vehicles to reflect light from theheadlights of the vehicle immediately behind it, for examples, theheadlights of vehicle [0. These conventional reflectors are of theretrodirective type, that is, reflectors which are constructed toreflect light impinging thereon from a distant source back in thegeneral direction of this incident source irrespective, within limits,reflect electromagnetic angle of incidence frequency the impinginglight. These reflectors are described and shown in greater detail inU.S. Pat. No. 2,205,638.

As shown in FIG. 2, the reflectors l6 and 18 comprise a plurality ofoptical corner cubes 26, each of which has three mutually perpendicularplanes or surfaces 28, 30 and 32. As shown more particularly in FIG. 3,light rays entering the flat surface of these reflectors, which facestoward the rear of the vehicle 20, will reflect light back in adirection parallel to the light incident thereon. They will also reflectelectromagnetic energy having a frequency lower than, and hence a wavelength longer than, the frequencies and wave lengths of the visibleelectromagnetic spectrum, provided these wave lengths do not exceed thedimensions of the lengths and widths of the plane surfaces 18, 30 and32. In conventional automotive vehicle reflectors, these dimensions areapproximately onesixteenth inch on rear tail light lens reflectors.Consequently, the transmitter 12 should be designed to transmitelectromagnetic energy having a wave length lower than one-sixteenthinch or approximately l.6 millimeters.

The applicant prefers to operate the transmitter so that it transmitselectromagnetic energy in the infrared region of the electromagneticspectrum, for example, the wave length of the energy transmitted may beapproximately I0,000 angstroms or 0.00l millimeters. This wouldcorrespond to a frequency of approximately 3X10 cycles per second. Theinfrared region of the electromagnetic spectrum is, of course, invisibleto the human eye and therefor will not interfere with the ordinaryfunction of the reflectors l6 and 18 on the vehicle 20 that isreflecting light from the headlamps of the vehicle immediately behindit.

The detecting and ranging system located in the vehicle comprising thetransmitter 12, the receiver 14, the computer 22 and the display device24 may be of a conventional type which will transmit electromagneticenergy having the wave lengths and frequency ranges given above.Additionally, this detecting and ranging system may be of the typedisclosed in my copending US. Pat. No. application Ser. No. 23,651,filed Mar. 30, I970.

As stated previously, the reflectors l6 and I8 reflect light impingingthereon from a source back in the general direction of the sourceirrespective, within limits, of the angle of incidence of the impinginglight.

Actual results of tests of this directivity of the reflection of theelectromagnetic energy impinging upon the reflectors I6 and IS, with theelements rotated at different angles both horizontally and verticallyabout a central axis are shown in FIG. 4. In FIG. 4, the numeral 1 onthe abscissa represents the strength of the light received back at thetransmitter when the light impinging upon either reflector 16 or 18 isnormal thereto. The curves on either side of this zero position indicatethe ratio of the amount of light received when either reflector 16 or IEis rotated through diflerent angles to the left or to the right orupwardly or downwardly about a central vertical axis or centralhorizontal axis to the amount of light received when the light incidenton either reflector is normal thereto.

It can be appreciated by an inspection of FIGS. I and 6 that the axis ofthe transmitter 12 and the axis of the receiver 14 are displaced adistance d measured along a line which is substantially perpendicular toor transverse to the longitudinal axis of the vehicle 10 and to itsdirection of movement. It has been found that by displacing the axis ofthe receiver 14 from the axis of the transmitter I2, the strength oramplitude of the signal received by the receiver 14 over the operatingrange of the detecting and ranging system of the present invention maybe substantially linearized.

Referring now to FIG. 5, there is shown a plot of the ratio of theamplitude or strength of a received signal at the receiver 14 to theamplitude or strength of a signal received when the vehicle is at amaximum distance within the operating range of the detecting and rangingsystem from the vehicle 10. The first curve designated A is a plot ofthis ratio when the axis of the receiver 14 is coaxial with respect tothe axis of the transmitter 12. This curve shows that this ratio variessubstantially inversely as the fourth power of the range. On the otherhand, if the distance (1" between the axes of the receiver I4 and thetransmitter 12 is approximately 6 inches, this ratio,

shown by the curve B, has a maximum value of approximately 100. Thiscontrasts dramatically to the maximum value of the ratio shown in curveA (here the axes of the transmitter and receiver are coaxial) ofapproximately 6Xl0". The curve C shown in FIG. 5 shows a plot of thisratio when the axis of the receiver 14 is displaced from the axis of thetransmitter 12 by a distance "d" equal to ten inches. In this case, themaximum value of this ratio is approximately 10. If the distance d" isincreased further, the maximum value of this ratio will decrease furtherand theoretically, could be reduced to a point where it is I throughoutthe range of operation of the detecting and ranging system.

FIG. 6 shows a schematic plan view of the receiver [4, the transmitter12 and either of the reflectors l6 and 18. The transmitter transmitselectrical energy along the axis or line 40 and it is designated by thewave action shown. The reflector, I6 or I8, reflects thiselectromagnetic energy back along the axis 40 with a certain angle ofspread so that a small portion of the electromagnetic energy is receivedby the receiver 14. This spread is caused by the fact that in the massproduction of the reflectors I6 and I8, the surfaces 28, 30 and 32 arenot located at precisely right angles, and therefor, the reflectedelectromagnetic energy is not truly directive, but is spread somewhat sothat the receiver 14 may pick a portion of this reflectedelectromagnetic energy. By separating the axis of receiver I4 from theaxis of the transmitter 12 in a direction substantially transverse tothe longitudinal axis of the vehicle, to the direction of movement ofthe vehicle and to the direction of propagation of the electromagneticenergy from the transmitter I2, the signal received by the receiver 14is substantially linearized in accordance with the curves B and C ofFIG. 5.

The present invention therefor provides a reliable uncomplicatedmechanical automatic gain control for a high frequency detecting andranging system. This mechanical automatic gain control thereby reducesthe variations in the magnitude or strength of the signal received atthe receiver of the system due to variations in range to a target.Consequently, the sophisticated electrical circuitry, which is usuallyand normally employed to overcome the problems associated with handlingwide variations in the amplitude or strength of received signals, iseliminated.

I claim:

1. A high frequency detecting and ranging system for use in anautomotive vehicle, comprising a transmitter and a receiver, saidtransmitter mounted on said automotive vehicle in a position to directelectromagnetic energy having a wave length in the optical region of theelectromagnetic spectrum in the direction of forward movement of thevehicle and onto a target comprised of a pair of spaced opticalretroreflectors of a preceding vehicle, said receiver being mounted onsaid automotive vehicle and separated from said transmitter so that thereceiver is displaced from the transmitting axis of said transmitter bya predetermined distance whereby said receiver receives electromagneticenergy having a limited ratio in strength as the range between thesystem and the target changes.

2. The combination of claim I in which said predetennined distance ismeasured in a direction transverse to the longitudinal axis of saidautomotive vehicle.

3. The combination of claim 2 in which said transmitter and receiver arelocated in a plane substantially transverse to said longitudinal axisand the direction of movement of said vehicle.

4. In an automotive detecting and ranging system, an automotive vehicle,a transmitting means mounted on said antomotive vehicle for directingelectromagnetic radiation having a wave length between about 1.6 mm. and4 l0 mm. in a direction of forward movement of said automotive vehicle,a receiving means mounted on said automotive vehicle in a positiondisplaced from the axis of said transmitting means, a target forreceiving and reflecting the electromagnetic energy transmitted by saidtransmitting means, said target comprising said receiving means fromsaid transmitting means is measured in a direction transverse to thelongitudinal axis of the automotive vehicle.

7. The combination of claim 5 in which the limited ratio in strengthvaries inversely as a function of the displacement of said receivingmeans from the axis of said transmitting means.

8. The combination of claim 7 in which the wave length of theelectromagnetic radiation falls in the nonvisible infrared region of theelectromagnetic spectrum.

1. A high frequency detecting and ranging system for use in anautomotive vehicle, comprising a transmitter and a receiver, saidtransmitter mounted on said automotive vehicle in a position to directelectromagnetic energy having a wave length in the optical region of theelectromagnetic spectrum in the direction of forward movement of thevehicle and onto a target comprised of a pair of spaced opticalretroreflectors of a preceding vehicle, said receiver being mounted onsaid automotive vehicle and separated from said transmitter so that thereceiver is displaced from the transmitting axis of said transmitter bya predetermined distance whereby said receiver receives electromagneticenergy having a limited ratio in strength as the range between thesystem and the target changes.
 2. The combination of claim 1 in whichsaid predetermined distance is measured in a direction transverse to thelongitudinal axis of said automotive vehicle.
 3. The combination ofclaim 2 in which said transmitter and receiver are located in a planesubstantially transverse to said longitudinal axis and the direction ofmovement of said vehicle.
 4. In an automotive detecting and rangingsystem, an automotive vehicle, a transmitting means mounted on saidautomotive vehicle for directing electromagnetic radiation having a wavelength between about 1.6 mm. and 4 X 10 4 mm. in a direction of forwardmovement of said automotive vehicle, a receiving means mounted on saidautomotive vehicle in a position displaced from the axis of saidtransmitting means, a target for receiving and reflecting theelectromagnetic energy transmitted by said transmitting means, saidtarget comprising the optical reflectors positioned on the rearwardlyfacing portion of a preceding automotive vehicle, said opticalreflectors including means for directionally reflecting light back tosaid transmitter in a direction along the transmitting axis thereofwhereby said receiving means receives electromagnetic energy having alimited ratio in strength as the range between the system and the targetchanges.
 5. The combination of claim 4 in which the wavelength of theelectromagnetic radiation falls in the nonvisible infrared region of theelectromagnetic spectrum.
 6. The combination of claim 4 in which thedisplacement of said receiving means from said transmitting means ismeasured in a direction transverse to the longitudinal axis of theautomotive vehicle.
 7. The combination of claim 5 in which the limitedratio in strength varies inversely as a function of the displacement ofsaid receiving means from the axis of said transmitting means.
 8. Thecombination of claim 7 in which the wave length of the electromagneticradiation falls in the nonvisible infrared region of the electromagneticspectrum.